Pregnancy due date calculator
The estimated due date, how far along you are today and when each trimester starts.
Result
Enter a date.
- Estimated due date
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- Today you are
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- Trimester
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- Days to go
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- Second trimester starts
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- Third trimester starts
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What this calculation assumes
- Pregnancy is counted from the first day of the last period, about two weeks before conception, so a 40-week pregnancy is 38 weeks after conception.
- Only about 1 in 25 babies arrives on the due date; most are born within two weeks either side. An early ultrasound dating scan is more accurate than any date-based estimate.
- This is general information, not medical advice. Your midwife or doctor will confirm the dates.
How a due date is estimated
Due date = LMP + 280 days + (cycle length − 28)
Pregnancy is dated from the first day of the last menstrual period (LMP), about two weeks before ovulation and conception. Naegele's rule adds 280 days (40 weeks) to that date. For a cycle longer or shorter than 28 days, ovulation shifts by the same amount, so the due date moves too: a 32-day cycle adds 4 days.
From a known conception date the due date is 266 days (38 weeks) later. After IVF it is 263 days after a day-3 embryo transfer or 261 days after a day-5 (blastocyst) transfer.
Weeks and trimesters
Weeks of pregnancy are counted from the LMP, so at conception you are already about 2 weeks pregnant. The first trimester runs to the end of week 13, the second from week 14 to the end of week 27, and the third from week 28 until birth.
Questions people ask
How likely is it that the baby arrives on the due date?
Only about 4% of babies are born on their due date. Most arrive between 38 and 42 weeks, and a first baby is a little more likely to come after the date.
Why did my ultrasound give a different date?
A first-trimester scan measures the baby directly and is more accurate than dating from a period, especially if your cycles are irregular. Midwives and doctors usually change the due date when the scan differs by more than about a week.
Can I use this if I do not know my last period?
Use the conception or transfer date if you know it. Otherwise an early ultrasound is the reliable way to date the pregnancy.